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Design >> Analog Design >> problems about filter solution v8.1 software
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Message started by baohulu on Sep 11^th, 2009, 11:49pm

Title: problems about filter solution v8.1 software
Post by baohulu on Sep 11^th, 2009, 11:49pm

hi, all
I use filter solution8.1 to synthesize a chebyshev II filter, which is in digital domain, for example, passband 1Hz, sampling clock 64Hz, and stopband ratio 1.5, then see its frequency response. as I know, its spectrum should be from -32Hz to +32Hz, when repeat it. however, in this software, its spectrum is from 0 to 64Hz, why?

Title: Re: problems about filter solution v8.1 software
Post by buddypoor on Sep 12^th, 2009, 8:22am

Because the program reflects reality !
There are no negative frequencies in reality !
It is only a mathematical "trick" to use neg. frequencies during formulation and calculation of the fourier transform (based on EULER´s formulas).
As a result, you have 2 alternatives: spectrum from -x to +x with amplitudes A or from 0 to 2x with amplitudes 2A.

Title: Re: problems about filter solution v8.1 software
Post by Berti on Sep 15^th, 2009, 2:40am

SSB spectrum is the frequency from 0 to +x with 2x the amplitude (0..32Hz). Why should the frequency go up to 2x? Do I miss something?

Cheers

Title: Re: problems about filter solution v8.1 software
Post by buddypoor on Sep 15^th, 2009, 2:55am

Berti wrote on Sep 15^th, 2009, 2:40am:

SSB spectrum is the frequency from 0 to +x with 2x the amplitude (0..32Hz). Why should the frequency go up to 2x? Do I miss something?
Cheers

No, Berti, you didn´t miss something.
But I was wrong, sorry. It was a mixture of typing/thinking error.
Of course, the spectrum goes only up to +x.
Thanks, regards